The invention relates to a method and plant for the treatment of contaminated soils and similar material in general, and in particular of coke-oven locations, by removal, decontamination and refilling of the place of removal with purified earth, in which the material removed is dried, possibly after a preliminary treatment, and then treated thermally with a high temperature.
For the elimination of deposits in rivers it is known to dredge them and feed the material to a rotating tubular kiln plant after effecting a preliminary treatment which consists of comminution in a crusher and screening. The rotating tubular kiln plant consists of two rotating cylindrical drums arranged one behind the other, the first of which operates as drying drum for the pre-drying of the material. The second rotating tubular kiln as seen in the direction of flow of the material is fired with an open flame which acts directly on the solids to be cleaned at temperatures between 400.degree. C. and 800.degree. C. Purified earth is removed from the rotating tubular kiln and returned to the place from which it has been removed.
The waste gases formed in the rotating tubular kiln plant, after removal of the dust contained therein, are heated in a combustion chamber with separate burner to a temperature of about 1200.degree. C. and thus decontaminated. After cooling and filtering, the purified waste gases are discharged into the atmosphere. A part of the waste gases are fed to the rotating cylindrical drying drum in order to intensify the drying process and improve the energy balance.
The known method has the disadvantage that the preliminary treatment by crushing and screening is not sufficient to assure uniformly small particle sizes of the contaminated material so that the following drying method step is also ineffective. "Complete cooking" of the material is not assured.
In the following method step consisting of the direct action of a flame on the solid material in the rotating tubular kiln, there is the disadvantage that there is not a uniform action of temperature but rather there are formations of strands of cold gas which lead to untreated strands of solids in the material removed, which is thus only inadequately cleaned. In principle, there is the problem upon using rotating tubular kilns for the drying and thermal treatment that considerable leaks occur at the individual rotating kilns between the stationary and rotating parts so that either the entrance of air resulting in an impairment of the energy balance must be feared or break-outs of air occur which result in the giving off of contamination-loaded gases to the environment. Any discharge of injurious substances into the surroundings must, however, be avoided. Finally, the temperatures obtained in a rotating tubular kiln are not sufficient to decompose all injurious substances, so that the earth cleaned in this way no longer satisfies modern requirements as to the protection of the environment. Finally the return of cleaned hot off-air to the drying drum which is effected in a partial stream behind the second burner is inadequate from an energy standpoint.